Seals are used to prevent leakage between two environments. Seals can be used, for example, to retain a fluid, separate fluids or to prevent the transmission of particulate contaminants from one environment to another.
Dynamic seals are used to seal passages between machine components that move relative to each other, either linearly or in the circumferential direction. There are various types of dynamic seals, including packing and piston seal rings, which are used for linear or oscillating movements. However, the most common seal is the radial shaft seal, which is used in a wide variety of applications in all branches of industry.
Dynamic seals are employed to retain lubricant, prevent water ingress and to prevent particulate, such as grit, contamination of the contact surfaces between the machine components (for example, the contact surfaces between the rolling elements and inner and/or outer rings of a rolling element bearing). However, as will be appreciated, friction during use leads to wear on the seal which will eventually lead to failure of the seal. In addition, the friction may reduce the efficiency of the device in which the dynamic seal is employed. For example, high levels of friction are generated within a shaft bearing as a result of the sliding contact between the surfaces of the metal shaft and the rubber bearing seal itself. Accordingly, there is a need for a dynamic seal (such as a dynamic bearing seal) exhibiting a low coefficient of friction. Such a seal would result in substantial energy savings, and would also be less likely to fail prematurely due to accelerated heat ageing of the seal.
Elastomer seals have remained popular for a number of dynamic sealing applications by virtue of a number of beneficial properties including good sealing performance, resistance to oils at elevated temperatures and low cost. However, one drawback is the necessity to maintain constant lubrication to avoid the high friction experienced when elastomers are run dry or in a starved condition. Traditionally, two alternative methods of lubrication are adopted for such seals: oil lubrication and grease lubrication. Oil lubrication enables the seal to be run at higher speeds with typically lower friction. However, it also necessitates the use of a more elaborate and expensive pumping system in order to ensure that a layer of lubricating oil is maintained at the contact surface. Grease lubrication offers lower cost and convenience but typically offers a slightly lower performance and may require changing during the lifetime. Grease systems commonly show a limited lifetime as a consequence of the grease being mobile in the vicinity of the sealing surface causing eventual starvation of lubricant.
There is a desire for a seal that will overcome, or at least mitigate, some or all of the problems associated with the seals of the prior art or at least a useful or optimized alternative.